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Manual Reference Pages  - Clan (3)

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Carp::Clan - Report errors from perspective of caller of a "clan" of modules

CONTENTS

 carp    - warn of errors (from perspective of caller)

 cluck   - warn of errors with stack backtrace

 croak   - die of errors (from perspective of caller)

 confess - die of errors with stack backtrace

    use Carp::Clan qw(^MyClan::);
    croak "We’re outta here!";

    use Carp::Clan;
    confess "This is how we got here!";

This module is based on "Carp.pm from Perl 5.005_03. It has been modified to skip all package names matching the pattern given in the use statement inside the qw()" term (or argument list).

Suppose you have a family of modules or classes named Pack::A, Pack::B and so on, and each of them uses "Carp::Clan qw(^Pack::);" (or at least the one in which the error or warning gets raised).

Thus when for example your script tool.pl calls module Pack::A, and module Pack::A calls module Pack::B, an exception raised in module Pack::B will appear to have originated in tool.pl where Pack::A was called, and not in Pack::A where Pack::B was called, as the unmodified "Carp.pm" would try to make you believe :-).

This works similarly if Pack::B calls Pack::C where the exception is raised, etcetera.

In other words, this blames all errors in the "Pack::*" modules on the user of these modules, i.e., on you. ;-)

The skipping of a clan (or family) of packages according to a pattern describing its members is necessary in cases where these modules are not classes derived from each other (and thus when examining @ISA - as in the original "Carp.pm" module - doesn’t help).

The purpose and advantage of this is that a clan of modules can work together (and call each other) and throw exceptions at various depths down the calling hierarchy and still appear as a monolithic block (as though they were a single module) from the perspective of the caller.

In case you just want to ward off all error messages from the module in which you "use Carp::Clan, i.e., if you want to make all error messages or warnings to appear to originate from where your module was called (this is what you usually used to use Carp;" for ;-)), instead of in your module itself (which is what you can do with a die or warn anyway), you do not need to provide a pattern, the module will automatically provide the correct one for you.

I.e., just "use Carp::Clan; without any arguments and call carp or croak" as appropriate, and they will automatically defend your module against all blames!

In other words, a pattern is only necessary if you want to make several modules (more than one) work together and appear as though they were only one.

As a debugging aid, you can force "Carp::Clan to treat a croak as a confess and a carp as a cluck". In other words, force a detailed stack trace to be given. This can be very helpful when trying to understand why, or from where, a warning or error is being generated.

This feature is enabled either by importing the non-existent symbol ’verbose’, or by setting the global variable "$Carp::Clan::Verbose" to a true value.

You would typically enable it by saying

    use Carp::Clan qw(verbose);

Note that you can both specify a family pattern and the string verbose inside the "qw() term (or argument list) of the use statement, but consider that a pattern of packages to skip is pointless when verbose" causes a full stack trace anyway.

The "Carp::Clan routines don’t handle exception objects currently. If called with a first argument that is a reference, they simply call die() or warn()", as appropriate.

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